In case you weren't sure, grout is the gritty stuff that fills the gaps (called grout joints) between tiles. When properly mixed and applied, grout lasts for decades, which is why you want to choose the right product for your job and, just as important, the right color of grout. Most standard grouts work on ceramic, porcelain, stone and other types of tile; there's no special formulation called "ceramic tile grout." And that leaves your options wide open.
Sanded or Unsanded?
Ceramic tile grout comes in two main types: sanded and unsanded (or non-sanded), and it's important to choose the right type for your application. Sanded grout is for grout joints that are 1/8" wide or wider. The addition of sand in the mix helps prevent cracking. Unsanded grout is for joints smaller than 1/8".
Cement-based grout is the conventional option for ceramic tile grout and is still used in almost all household tile jobs. It uses Portland cement as a hardener and is available dry powder form that you mix with water. These days, most cement-based grouts are polymer-modified (or "polyblend"). This means the mix contains various latex admixtures for better adhesion, workability, stain-resistance and other characteristics. Cement-based grouts are the easiest to clean up and also the cheapest option for ceramic tile grout.
Urethane grout is fairly new to the general marketplace and offers some appealing advantages. For some, the nicest feature is that it's premixed; you scoop it right out of the bucket and onto to the tile. Made with polyurethane resins and polymers (not cement), urethane grout has great adhesive properties, is more flexible than cement-based grout and doesn't need to be sealed. Sanded versions (the only type currently available) can be used on joints as narrow as 1/16".
Epoxy grout is an industrial-strength blend made with two synthetic liquids mixed together, just like epoxy glue, with or without sand added. It's adhesion is unmatched, it never needs to be sealed and it's highly resistant to staining and even chemical spills. Used most often in commercial applications, epoxy grout is clearly the most durable choice for high-traffic areas of the house.
Before You Grout Your Tile...
No matter what type of ceramic tile grout you choose, you won't be happy with the results if the color isn't right. To see what the grout will really look like when it's cured, don't rely on manufacturers' samples or the wet mix itself. Instead, perform your own test by applying the grout between a few tiles stuck to a scrap board, and let the grout dry completely. Also apply a grout sealer, if applicable, since sealers add a slight sheen that can affect the look of the grout.
Too busy for DIY? Find a ceramic tile contractor in your area.